System for firing series-circuit blasting caps



March 28, 1967 M. D. PAIGE 3,311,788

SYSTEM FOR FIRING SERIES"CIRCUIT BLASTING CAPS Filed July 23, 1964 52onus. NON mo. LOAD 8 r Fig 5 Hg 3 7 5i s 2 I :32 I 3 E o O I I I o lo 20so 40 so so 10 so 90 Time in Milliseconds Fig 6 H 4 Time in MillisecondsMILTO J6 Z United States Patent 3,311,788 SYSTEM FOR FIRINGSERIES-CIRCUIT BLASTING CAPS Milton D. Faige, 36 De Kalb Place,Morristown, NJ. 07960 Filed July 23, 1964, Ser. No. 384,814 4 Claims.(Cl. 31780) The invention described herein may be manufactured and usedby or for the Government for governmental purposes Without the paymentto me of any royalty thereon.

The present invention relates to electrical blasting machines, and moreparticularly to a system for firing a plurality of blasting capsthereby, in a series circuit.

Blasting machines of the type referred to have been built and used formany years as is known, and include rotary electric generator meansgenerally manually-opis particularly true of the machines with thetwist-action key type drive.

To obtain safety of operation in the field through suflicient output,considerable effort has been made over the past years both by commercialorganizations as well as the government. Such efforts to the presenthave been concentrated mainly on increasing the total output capabilityof the generators. In a further effort to fi-re all caps in a series atthe same instant, such machines have also been provided with switchmeans in the output circuit which is closed mechanically near the end ofthe manual stroke or power application, and kept closed to pass currentto the caps when the generator speed is near maximum and after.

These and other known expedients have failed to attain the desired highdegree of reliability in firing series blasting circuits by machines ofelectric-generator manuallydriven type, which are practically the onlytype now in use. Furthermore it is known that the use is extensive, asindicated by the more than one-hundred million blasting caps used inthis country alone in one year. The Armed Forces use blasting machinesin considerable quantity for military and other applications, and havethe same problems in firing with a high degree of reliability. It isknown that presently available machines are never reliable in operationunder all conditions of operation in the field.

Therefore, it is a primary object of the present invention to provide animproved system for the safe firing of series connectedelectrically-activated (current ignited) blasting caps by manually(plunger or key) -operated electric-generator type blasting machines.

It is a further object of the present invention to provide an improvedsystem for firing series-connected blasting caps by machines of the typereferred to, which applies maximum electrical output thereto during aninitial time interval of relatively short duration, and thereby providesa relatively high degree of firing reliability in the field under allconditions of operation.

It has been found, in accordance with the invention, that the use of theutmost peak power or current output of the generator for a relativelyshort initial time interval must be assured for maximum reliability,rather than a current build-up and peak, as heretofore assumed andprovided for. Increase in the total output capability of the generatoror a consideration of a proper speed for switching does not and has notsolved the problem.

Firing failures, it has been found further, are due primarily, if notwholly, to lower than peak output at the critical time of initial outputto the firing circuit, and with a longer output period than iseffective. By taking pictures of oscilloscope readings of the currentoutput pulses of the machines in use, it was determined that the outputstarted from ten to forty milliseconds prior to peak output "ice . andcontinued well over the relatively short time interval 'of ten tofifteen milliseconds which has been found to be desirable for reliablefiring.

The initial output in such conventional systems are thus found to beover the minimum requirements for highly sensitive caps but under thatrequired for less sensitive ones, and results in ruptures of the serieselectrical circuit before excitation time has been completed on theslower caps. The resultant hazards, from unfired caps in the series,have always been a cause of injuries and worse.

It is, therefore, a still further object of the present invention, toprovide an improved system for firing seriescircuit blasting caps formanually-driven blasting machines, which may be adjusted in use orpreset at manufacture to assure maximum electrical output during aninitial ten to fifteen millisecond period and thereby provide a desiredsubstantially 99% firing reliability for 'the circuit in operation underany field condition.

Thus the machine and the switching control and circuit, as parts of thesystem, are coordinated to ensure mechanical presetting at manufactureor resetting in the field for the most effective and safe operation ofthe series circuit. This assures the maximum current peak output for theinitial brief period required, rather than the normal current build upand peak with sustained output for a longer period than is effective.

The invention will, however, be further understood from the followingdescription, when considered'with reference to the accompanying drawing,and its scope is pointed out in the appended claims.

In the drawing:

FIG. .1 is a schematic plan view of a system, including amanually-driven generator-type blasting machine and series cap-firingcircuit, embodying the invention;

FIG. 2 is a similar schematic view, in elevation and partly in section,of the machine of FIG. 1, taken on the section line 22, to show aconstructional and operational detail thereof in accordance with theinvention;

FIGS. 3 and 4 are graphs showing oscilloscope curves illustrating anoperational feature of the system of FIGS. 1 and 2, and

FIGS. 5 and 6 are schematic views, in the same elevational plane as FIG.2, of two modifications, in accordance with the invention, of theconstructional and operational detail shown therein.

Referring to the drawing and particularly to FIGS. 1 and 2, a blastingmachine 8 is provided with a manual operating handle 9 detachablymounted on a rotary operating shaft 10 for the machine. The shaft ismounted in suitable bearings as indicated at 11 to rotate in thedirection of the arrowed line in response to manual downward drivingmovement of the lever or handle 9, as viewed in FIG. 1, and drives theshaft 12 of an electric generator 13 in the machine to produce a pulseof operating current at the machine output terminals 14 and 15. Theoutput current pulse may be of extended duration as measured inmilliseconds and of rising, sustained and falling amplitude, as willhereinafter be described.

The driving connection between the shafts 10 and 12 is through a step-upgear train 16, common to such machines, and comprising in the presentexample, a segmental or half gear 1'7 mounted on the drive shaft 10 andmeshing with a smaller pinion gear 18. The latter is mounted on the sameshaft 19 with a larger drive gear 20 which, in turn, meshes with asmaller driven pinion gear a fixed bar 23, is provided to limit thismovement of the lever and gear segment. A suitable clutch 24 is providedto connect the pinion 21 and the generator shaft 12 only on theoperating stroke, whereby the handle may be returned to the startingposition without turning the generator shaft, as is conventional in suchmachines.

The electrical current output of the blasting machine is used toactivate or ignite a quantity of electrical blasting caps 27 asindicated, connected in electrical series in a firing circuit 28extending between the output terminals 14 and 15. Each cap includes acurrent-responsive fuzing element 29 which heats and burns or blows toignite the cap when the current is at a predetermined value. Some capsare more sensitive than others as explained hereinbefore. Hence the needfor peak current during the initial application of firing current to theseries string or circuit. More than one firing circuit of this type maybe connected to the terminals 14 and 15 of the machine, as isunderstood. While ten caps, as a normal number, are shown in the singleseries circuit of the present example, more or less may be employed,depending upon the generator capacity to provide the peak currentrequired for the brief initial time interval, which has been found to befrom four to fifteen milliseconds, for safe and effective firing, with ahigh degree of reliability, of all caps simultaneously.

Thus, in accordance with the invent-ion, and with reference to FIGS. 3and 4, oscilloscope records as shown, or

other indication of the output current build-up, sustained peak value,and decay, are primarily considered, rather than the generator speeds aswill be considered further herein. A switch-closing device, such as apin 32 on the segmental gear 17, is provided and adjusted in conjunctionwith a suitable switch or switch means 33 connected between thegenerator ;13 and one of the output terminals 14, for example, wherebythe point of firing current delivery to the caps 27 in the firingcircuit 28 is timed to obtain the desiredxmaximum or peak portion of theoutput response of the generator or machine during the initial four tofifteen milliseconds of the applied current.

In the circuit of the present example, and as indicated in FIG. 4, it isarranged for an effective, 1.98 amperes R.M.S. of firing current duringthe initial milliseconds of firing current application, allowingapproximately 0.2 millisecond for recording current build-up to peakafter switch closure. The time of closing is adjusted by changing switchand pin relation along the path of movement of the pin.

In the present example, the switch is adjustable and comprises twospaced, s-ubstantially-parallel, flat switch blades 34 and 35, of springmetal extending at their free ends from a pivoted insulating spacerblock or support means 36 into the path of movement of the pin 32 toclose a pair of contacts 37 between and carried by the blades, asindicated in FIG. 2, when the pin meets and moves the upper blade 34 (asviewed in the drawing). The time of closing is adjusted by moving theblades, in the directions of the arrowed lines from the position shown,about the pivot point of the block 36 to cause an earlier or laterclosing of the switch for peak initial output to the firing circuit asdescribed.

In the circuit connections for the switch, one generator output terminal38 is connected through a lead 39 to one terminal 40 of the switch,which is on the lower blade 35 in the preesnt example. The other switchterminal 41, on the upper blade 34, is connected through a lead 42 tothe main output terminal 14. The other main output terminal 15 isconnected directly with the remaining generator terminal 43 through aconnection lead 44.

A micro-switch 46, as shown in FIGS. 5 and 6, may be provided in placeof the switch 33 in the system of FIGS. 1 and 2. The usual depressibleswitch button 47 is positioned to be actuated by a suitable cam element4'8 mounted on the drive shaft 10 to move with the gear segment 17 andhandle 9 through the circular path indicated, over any angular range,such as the full degrees indicated in FIG. 5, or the limited rangeindicated in FIG.

6. In the first case the cam is clamped to the shaft and moves with itover the full range, or less, as set on the shaft. In the second case,an adjustable stop screw 49, mounted in a fixed support element 50, ismovable to determine the relative angular positions of the handle 9, orgear segment 17, and the cam or switch operating element 48 at the startof the operating stroke, and hence the precise time of closing of theswitch 46. The switch terminals 51 are connected, in practice, with theleads 39 and 42 in the circuit of FIG. 1, and the operation is otherwisethe same as for the switch 33.

Referring again to FIGS. 3 and 4, the timing of the system is such thatthe utmost peak output of the generator, as indicated by theoscilloscope current trace 55 in FIG. 4, is attained and applied to thefiring circuit over the brief initial time interval of 415 millisecondsas indicated. This is compared with the conventional controlled firingcurrent indicated by the oscilloscope trace 56 in FIG. 3, when the peakoutput is slow in attainment and too prolonged. Thus the initial outputrises over the minimum requirements for the highly sensitive caps, oneof which blows, and is under that required for the less sensitive onesfor an extended time as indicated. Thus the electrical firing circuit isruptured by one or two caps before excitation time has been completedfor the slower caps. The hazard from the unfired caps is thus a seriousproblem in blasting work with series firing circuits as normally used.

The adjusted cam control for peak switching has solved thislong-standing problem. A full firing current of over 1.5 amperes isapplied to the total of ten or any number of caps in the firing circuitfor a sufficient initial time interval to energize all (ten) before themost sensitive cap can rupture and break the series electrical circuit.This system gives approximately 99% reliability as desired. Theconstructional changes in existing equipments can be made at reasonablecosts and results in a greatly safer operation for all blasting machinesof this type, both for military as well as commercial applications.

It has also been shown that with the present system for firingseries-circuit blasting caps, there is a sufficient output timeinterval, or sustained peak level output following peak outputswitching, to efiectively fire the circuit before fall-off in thedriving power of the firing stroke.

I claim:

1. A system for firing series-circuit blasting caps with a high degreeof reliability, comprising in combination, an electric currentgenerator, electrical means providing a firing circuit output connectionwith said generator including a pair of output terminals, normally-openswitch means in said connection between the generator and one of saidterminals, movable means for manually driving said generator with alimited power stroke through a varying current range having a limitedsustained peak, said last-named means having an operating pin-likeelement affixed thereto and movable therewith in a predetermined pathfor effecting closure of said switch means in response to each powerstroke of the generator driving means in timed relation to and duringsaid peak in the output current range.

2. A system for firing a plurality of electric currentresponsiveblasting caps of differing sensitivity to firing current magnitudes andconnected inelectrical series relation, comprising in combination, anelectric current generator having a peak current output effective tofire said series-connected caps all at the same time, means including amovable manual operating element and a step-up gear train connectingsaid element and the generator for driving said generator with a limitedmovement of said element to provide said peak current output over apredetermined limited time interval, a normally-open switch connected incircuit with said generator to control the current output therefrom,means connected with said manual operating element and responsive tomovement thereof to drive said gear train and generator for effectingclosure of said switch, and means for adjusting the timing of the switchclosure to fall at said current peak and within said limited timeinterval, thereby to apply peak initial firing current to said seriesconnected caps in the operation of said system and provide a high degreeof reliability.

3. A system for firing series-connected blasting caps of differingsensitivity to firing current magnitudes, comprising in combination, anelectric current generator, electrical means providing a firing circuitoutput connection with said generator including a pair of outputterminals, normally-open switch means in said connection between thegenerator and one of said terminals, movable means for manually drivingsaid generator with a limited power stroke through a varying currentrange having a limited sustained peak, said last-named means having acam element affixed thereto and movable therewith to effect closure ofsaid switch means in response to each power stroke of the generatordriving means in timed relation to and during said peak in the outputcurrent range, said degree of reliability in the firing ofseries-connected blasting caps in firing circuits connected therewith.

4. A system for firing a plurality of blasting caps in a single firingcircuit with a high degree of reliability, comprising in combination, anelectric current generator, means providing an electrical outputconnection with said generator including a pair of output terminals forsaid firing circuit, normally-open switch means in said connectionbetween the generator and one of said terminals, means for efiectingclosure of said switch means, said last named means being aflixed to andcarried by manually movable means for driving said generator, saidlast-named manually movable means being adapted to progress with alimited power stroke through a varying generated current range having asustained peak of from 4 to 15 milliseconds duration, said sustainedpeak being provided to insure substantially simultaneous firinginitiation of all blasting caps in said firing circuit, and therebypreventing the individual initiation of any one more sensitive cap andhence the cut off of the remainder of said caps due to the resultantopening of said circuit.

References Cited by the Examiner UNITED STATES PATENTS 2,129,835 9/1938Schafiler-Glossl 317- X 2,546,686 3/1951 Bickel et al. 3 l780 X2,618,755 11/1952 Bussey 3l7-80 X 2,844,747 7/1958 Schafiier-Glossl310-69 2,902,627 9/ 1959 Colten 317-80 RICHARD M. WOOD, PrimaryExaminer.

V. Y. MAYEWSKY, Assistant Examiner.

1. A SYSTEM FOR FIRING SERIES-CIRCUIT BLASTING CAPS WITH A HIGH DEGREEOF RELIABILITY, COMPRISING IN COMBINATION, AN ELECTRIC CURRENTGENERATOR, ELECTRICAL MEANS PROVIDING A FIRING CIRCUIT OUTPUT CONNECTIONWITH SAID GENERATOR INCLUDING A PAIR OF OUTPUT TERMINALS, NORMALLY OPENSWITCH MEANS IN SAID CONNECTION BETWEEN THE GENERATOR AND ONE OF SAIDTERMINALS, MOVABLE MEANS FOR MANUALLY DRIVING SAID GENERATOR WITH ALIMITED POWER STROKE THROUGH A VARYING CURRENT RANGE HAVING A LIMITEDSUSTAINED PEAK, SAID LAST-NAMED MEANS HAVING AN OPERATING PIN-LIKEELEMENT AFFIXED THERETO AND MOVABLE THEREWITH IN A PREDETERMINED PATHFOR EFFECTING CLOSURE OF SAID SWITCH MEANS IN RESPONSE TO EACH POWERSTROKE OF THE GENERATOR DRIVING MEANS IN TIMED RELATION TO AND DURINGSAID PEAK IN THE OUTPUT CURRENT RANGE.